The present invention relates to a small-sized and inexpensive semiconductor laser suitable for use as a pickup light source in, for example, DVDs (digital video disks) and DVD-ROMs. More particularly, it relates to a stem type semiconductor laser which can be formed in a small outside dimension even if a laser chip for DVDs is large-sized.
The stem type semiconductor laser used as conventional pickups for CDs has such a structure as shown in FIG. 7. Specifically, a stem 20 is used which is produced by forming a metallic material such as iron by cold forging, raising a part of the center portion of a base 21 to form a heat sink section 22 and fixing leads 23 and 25 by using a glass 26 or the like. A laser chip 31 is mounted on the heat sink section 22 through a submount 34 made of a silicon substrate or the like. One electrode (backface electrode of the chip 31) is electrically connected to the lead 23 through a relay portion 38 of the submount 34 by a wire 33 and another electrode is connected to the submount 34 through a wire 33 and is also electrically connected to a common lead 24 by way of the heat sink section 22 and the base 21 via the backface of the submount 34. 32 represents a light receiving element for monitor. One electrode of the light receiving element 32 is electrically connected to a lead 25 through a wire 33 and another electrode is electrically connected to the common lead 24 through the submount 34, the heat sink section 22 and the base 21. The periphery of these portions is covered by a cap 35 to form the semiconductor laser. A through-hole 35a is formed in the center of the top of the cap 35 to transmit light emitted from the laser chip 31 and a glass plate 36 is sealed by an adhesive 37.
In this structure, although the heat sink section 22 must be formed between the leads 23 and 25, the leads 23 and 25 must be sealed by the glass 26 or the like. It is therefore impossible to decrease the diameter of the stem 20. Hence, only semiconductor lasers having an outside dimension of about 5.6 mm xcfx86 have been manufactured.
On the other hand, as shown in FIG. 8, there is a type obtained by processing a plate-like body by drawing to form a ring 27 and a pedestal portion 28 to be a heat sink into one united body, directly sealing leads 23 and 25 within the ring 27 by using a glass 29 or the like to form a stem 20 and a cap 35 is allowed to cover the periphery of the stem 20 by press fitting. By making the semiconductor laser having such a structure, it is unnecessary to form the heat sink section directly on the base of the stem and also a space used to weld the cap. Hence a semiconductor laser with a diameter of about 3.3 mm xcfx86 is produced. In FIG. 8, the same parts as in FIG. 7 are represented by the same symbols and the explanations of these parts are omitted.
As to a light source used for the conventional pickups for CDs, the size of a laser chip used in the light source is about a 0.25 mm by 0.25 mm square and operating current is small. Even if a semiconductor laser having the structure shown in the aforementioned FIG. 8 is used as the light source, no problem arises because the operating current is small to reduce the calorific value. On the contrary, a laser chip for DVDs is as large as about a 0.25 mm by 0.5 mm square and operating current is about two times that of the chips for CDs. There is the problem that insufficient heat dissipation results in no emission of the laser chip. Because of this reason, it is necessary to make the heat sink section as large as possible to thereby promote heat dissipation. Moreover, in the structure shown in FIG. 8, it is necessary to form a thick solder plating on the surface of the stem since the cap is fitted by press fitting, giving rise to the problem that a thick solder plating is formed on a lead, leading to difficult wire bonding.
While, for pickups used to detect signals of, for example, CDs or DVDs, very thin types are required along with the development of light-weight, thin and small-sized electronic equipment as typified by recent note-type personal computers. As a semiconductor laser used side-wise in a pickup, one having a small diameter is needed. For even types which are made to have a large chip size and must have good heat dissipation characteristics, it is desired to decrease the outside diameter to about 3.3 mm xcfx86 or less.
The present invention has been conducted in view of the aforementioned situation and has an object of providing a semiconductor laser having a small outside diameter, the semiconductor laser being improved in heat dissipation characteristics by making a heat sink section large even if a laser chip having a large chip size and a large calorific value is used.
Another object of the present invention is to make such an optical pickup as used in a note type personal computer thinner and to provide an optical pickup device which allows electronic equipment to be thinner.
A semiconductor laser according to the present invention comprises: a stem which is secured such that at least two leads are projected from both sides; a support section disposed on one side bottom (lead-fixed section) of the stem; a heat sink section formed on the upper portion of the support in a wide width extending to the side of the two leads; and a laser chip secured to the heat sink section.
Here, the meaning that the heat sink section is formed in a wide width extending to the side of the two leads implies either one or both of the case where the support section disposed between the two leads extends in the direction of the width of the leads and the case where the support section disposed behind the lead extends to the side of the front lead (in a direction perpendicular to the direction of the width of the leads). It is to be noted that the portion formed in a wide width may be wide in width either such that it covers the upper portion of the top of the lead or to the extent that it covers the glass portion securing the leads though it uncovers the top of the leads.
This structure ensures that even if the support section is limited in width by the interval between the leads and the like on a plan view (viewing the stem from the above), the volume of the heat sink section can be secured even if the interval between the leads is narrow because in the structure, the heat sink section is overlapped on the leads (including the glass portion securing the leads). As a result, a heat sink section enough to dissipate heat can be provided even if the interval between the leads is made narrow to obtain a semiconductor laser with an outside diameter of 3.3 mm xcfx86. Also, even laser chips, such as those for DVDs, having a large chip size and a large calorific value can be made into small packages. That is, conventional semiconductor lasers of this type are manufactured based on the idea that a heat sink section and a support section have the same widths and the heat sink portion and leads are arranged such as in line on a plan view; therefore, a restriction is imposed on the interval of the leads in the stem and such a restriction that the heat sink section cannot be made large is imposed. However, by adopting such an idea that the heat sink section is extended and made large so as to overlap on the leads on a plan view, even semiconductor lasers for DVDs having a large chip size and a large calorific value could be formed into a small-sized one with an outside diameter of about 3.3 mm xcfx86.
Preferably the stem is formed by securing the at least two leads to the through-hole of the metal base with an insulated material, the support section is integrated with the base and the heat sink section is stuck to the support section. This structure makes it possible to use a copper material or the like having high heat conductivity for the heat sink section.
Preferably the aforementioned at least two leads are secured to the through-hole of the metallic base with an insulated material to form the stem and the support section and the heat sink section are integrated with the base. By this structure, dimensional accuracy is bettered and the assembly is made easy.
Preferably the support section and the heat sink section are formed as an integral subject by using a metallic material, for example, a metal block or plate material and the support section of the integral subject is secured to the base of the stem. This structure makes the production step of the stem easier.
The stem may be a type which is formed by sealing at least two leads in a cylinder ring with an insulated material. Even if this type is used, a semiconductor laser having a laser chip, such as those for DVDs, having a large chip size and a high calorific value can be made because of the provision of the heat sink section which is formed in a wide width and improved in heat dissipation.
An optical pickup device according to the present invention comprises: a semiconductor laser; a diffraction grating; a beam splitter which separates the light emitted from the semiconductor laser from the light returned by being reflected on the disk; a collimator lens which collimates beam from the semiconductor laser; a reflecting mirror which bends the beams from the semiconductor laser at a right angle; an objective lens which focuses the beam on the disk; and a light detector which detects the light reflected from the disk and separated by the beam splitter; wherein the semiconductor laser comprises the aforementioned semiconductor laser.